1. Field of the Invention
This invention relates to a cationically polymerizable composition excellent not only in storage stability but also in colorant-dispersion stability.
2. Description of the Related Art
Ink compositions, which undergo radical polymerization and curing when irradiated with active energy beams such as ultraviolet rays, have been known as quick-drying printing inks. These ink compositions, however, have given rise to a problem of being subjected to curing inhibition in the presence of oxygen.
Thus, in recent years, there have been proposed ink compositions which undergo cationic polymerization and curing when irradiated with active energy beams. As these ink compositions, have been proposed those including an oxetane compound, a cationic photopolymerization initiator and a pigment, and further including an epoxy compound when needed (Japanese Patent Laid-Open No. 8-143806). Cationic polymerization is advantageous in that it is not inhibited by oxygen, it does not have to be performed in an inert atmosphere, and it can be performed quickly and completely in the air, since it is initiated in the presence of cation generated from a cationic polymerization initiator when the initiator is irradiated with ultraviolet rays or the like.
However, when cationically polymerizable compounds such as oxetane compounds and epoxy compounds are stored with a cationic polymerization initiator added thereto for a long period of time, cation can sometimes be generated spontaneously from the cationic polymerization initiator even in a state of ultraviolet rays being blocked, and there sometimes occurs a problem that the cation initiates the polymerization of the cationically polymerizable compounds, causing thickening and gelation.
In order to solve such a problem, Japanese Patent Laid-Open No. 2000-186079 has proposed to improve the storage stability of the oxetane compound without deteriorating ring opening polymerizability of the oxetane compound by adding a basic compound, for example, a basic organic compound such as an amine to the oxetane compound, and has described, as such an amine, octylamine, naphthylamine, xylenediamine, dibenzylamine, diphenylamine, dibutylamine, dioctylamine, dimethylaniline, quinuclidine, tributylamine, trioctylamine, tetramethylethylenediamine, tetramethyl-1,6-hexamethylenediamine, hexamethylenetetramine and triethanolamine.
However, even the addition of such an amine cannot necessarily produce a sufficient effect of inhibiting the cationically polymerizable compound from polymerizing, and particularly when the cationically polymerizable compound is a mixture of an oxetane compound and an alicyclic epoxy compound, its storage stability is often unsatisfactory. Moreover, when a colorant is added thereto so that it is used as an ink, the colorant sometimes agglomerates to deteriorate its dispersion stability.
Accordingly, an object of this invention is to provide a technique which permits improvement in storage stability of a cationically polymerizable compound containing a cationic polymerization initiator, and in addition, ensures dispersion stability of colorants.